Get started with GAWK: AWK language fundamentals
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1. Get started with GAWK AWK language fundamentals Page 16 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks awk BEGIN ORS print END print n sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly More GAWK variables The NF variable contains the number of fields in the current record Using NF references its numeric value while using SNF references the contents of the actual field itself So if a record has 100 fields print NF outputs the integer 100 while print 100 outputs the same thing as print NF the contents of the last field in the record The NR variable in turn contains the number of the current record When the first record is being read its value is 1 when the second record is being read it increments to 2 and so on Use it in an END pattern to output the number of lines in the input awk END print Input contains NR lines sample Linjoine ComeEecsins S lames Note If the print statement above had been placed in a BEGIN pattern the program would have reported that its input contained 0 lines because the value for NR at the time of execution would be 0 as no records of input would have been read yet Use NR to print the field relative to the current record number awk print NR SNR sample Heigh ho friendship the2. WODHA Take a look again at Figure 4 and see the values for Field 1 in the first record Field 2 in the second record and Field 3 in the last record Compare this with your program output Try listing the number of fields for each record and the value of the last field awk print Record NR has NF fields and ends with NF sample Record 1 has 7 fields and ends with holly Record 2 has 8 fields and ends with folly Record 3 has 4 fields and ends with holly There are a handful of special GAWK variables that are frequently used Table 2 lists them and describes their meaning Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 17 of 23 developerWorks iobm com developerWorks Table 2 Common GAWK variables Variable Description NF This variable contains the number of fields per record NR This variable contains the number of the current record FS This variable is the field separator RS This variable is the record separator OFS This variable is the output field separator ORS This variable is the output record separator FILENAME This variable contains the name of input file being read IGNORECASE When IGNORECASE is set to a non null value GAWK ignores case in pattern matching Section 6 GAWK pattern matching In GAWK the pattern matching facility is similar to that of the egrep command To output
3. Free Software Foundation either version 2 of the License or at your option any later version This program is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE See the GNU General Public License for more details You should have received a copy of the GNU General Public License along with this program if not write to the Free Software Houndalon ainei oo Lemples Pilkac Suite 330 Boston MA 02111 1307 USA Now that you have a working GAWK installation and you know how to call it you re ready to begin programming The next section describes basic AWK programming concepts Section 3 Understanding records fields and rules Learn the basics of the AWK programming language records fields and rules Elements of an AWK input file AWK works on text input and this text can be a file or the standard input stream which it sorts into records and fields An AWK record is a single continuous length of input data on which AWK works Records are bounded by a record separator which is a character string and defined as the RS variable see Change the record separator By default the value of RS is set to a newline character so the whole lines of input are considered records for the default behavior of AWK Records are read continuously until the end of the input is reached Figure 1 shows how input data
4. S awk BEGIN FS print 3 sample unto the green holly Try comparing the fields in the output you get with the fields listed in Figure 4 But the field separator doesn t have to be a single character Try using a phrase awk BEGIN FS Heigh ho print 2 sample sing heigh ho unto the green holly In GAWK the field separator can be any regular expression To make each input character its own field give Fs a value of null Capitalization counts The example above only matches one separator in the entire file but the following example matches the same phrase regardless of case awk BEGIN FS Hh eigh ho print 2 sample galing the holly You can also change the field separator from the command line by specifying it as a quoted argument to the F option awk F print 2 sample heigh ho unto the green holly most loving mere folly Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 15 of 23 developerWorks iobm com developerWorks heigh ho This functionality makes it easy to create one liners that can parse files such as etc passwd where fields are delimited by a colon character You can easily pull out a list of full user names for example awk F print 5 etc passwd Change the record separator As with the field separator you can change the record separato
5. is broken into records Figure 1 AWK input data split into records Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 5 of 23 developerWorks ibm com developerWorks Onca Each record in turn can be broken down further into individual chunks called fields Like records fields are bounded The default field separator is any amount of whitespace including tab and space characters So by default lines of input are further broken down into individual words any groups of characters separated by whitespace You can reference the fields of a record by field number beginning with 1 You can call the last field in each record either by its number or with the special variable NF which contains the number of fields in the current record You can reference an entire record including all of its fields and field separators by a field number of 0 Figure 2 shows the contents of such a field a single record of AWK input data as it is divided into its composite fields Figure 2 Fields of an AWK record Field 0 Fe es Fean Note AWK provides ways to split the elements of a field into its character components but that s outside the scope of this tutorial Know the rules AWK programs consist of rules which are patterns followed by actions separated by newlines When AWK follows a rule it searches the input records for matches to the given patt
6. on fields and records with AWK tabular data is easy to parse manipulate and reformat using just a few simple commands You can use shell redirection to direct the reformatted output to a new file or pass it down a pipeline Working as a filter this functionality becomes useful in conjunction with other commands For example this command modifies the default output of a date so that it prints in a day month year format date awk print 3 2 6 29 Nov 2006 Change the field separator The fields in the examples so far have been separated by space characters That s the default behavior any number of space or tab characters and you can change Get started with GAWK AWK language fundamentals Page 14 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks it The value of the field separator is contained in the Fs variable Like any variable in AWK it can be redefined at any time in a program To use a different field separator for the entire file redefine it ina BEGIN statement Print the first field of the sample data with a field separator of an exclamation point S awk BEGIN FS print 1 sample Heigh ho Most friendship is feigning most loving mere folly Then heigh ho the holly Note the differences when printing the second and third fields S awk BEGIN FS print 2 sample sing heigh ho
7. only records that match a pattern give that pattern in the rule enclosed in slash characters Match patterns in input records To match a single pattern give it in a rule awk green print sample Heigh ho sing heigh ho unto the green holly You re not limited to strings the pattern can be any extended regular expression Try matching records in the sample input that contain two exclamation points with any amount of text between them S awk sample Heigh ho sing heigh ho unto the green holly Unlike grep you can also specify hex and decimal values of ASCII characters in your search To give hex values use the format xNN where NN is the hex value of the character in question To give decimal values use the format xxx where Xxx is the decimal value of the character Get started with GAWK AWK language fundamentals Page 18 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks This functionality is good for matching extended or non printing characters such as the BELL character a literal Ctrl G which you can match with 007 as the pattern However AWK does not work on binary files Match patterns in fields To match a pattern in a specific field as opposed to in the entire record give the field and use the operator which means contains and then give the pattern Sfield pattern The operator works in the opposit
8. prepare your GAWK installation so that you can begin programming The AWK language AWK is the name of the programming language itself written in 1977 Its name is an acronym for the surnames of its three principal authors Drs A Aho P Weinberger and B Kernighan Because AWK is a text processing and pattern matching language it s often called a Get started with GAWK AWK language fundamentals Page 2 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks data driven language the program statements describe the input data to match and process rather than a sequence of program steps as is the case with many languages An AWK program searches its input for records containing patterns performing specified actions on that record until the program reaches the end of input AWK programs are excellent for work on databases and tabular data such as for pulling out columns from multiple data sets making reports or analyzing data In fact AWK is useful for writing short one off programs to perform some feat of text hackery that in another language might be overkill In addition AWK is often used on the command line or with pipelines as a power tool Like Perl which it inspired AWK is an interpreted language so AWK programs are generally not compiled Instead the program scripts are passed to the AWK interpreter at run time Systems programmers find themselves immediately
9. quoting As a script Another way to run a GAWK program is to put it in a file and make it an executable script with the shebang command execution if your shell supports it Put the program in a GAWK script file called awkat make it executable and try running it with the sample file as shown in Listing 6 Listing 6 Running the simple program as an executable Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 11 of 23 developerWorks iobm com developerWorks cat gt awkat usr bin awk f print Ctrl d chmod u x awkat awkat sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly Section 5 Manipulating records and fields When GAWK reads in a record it stores all the fields of that record in variables You can access each field by a followed by the field number so 1 references the first field 2 references the second and so on all the way to the last field of the record Figure 4 shows the sample text delineated in the default records and fields Figure 4 Sample file broken down into AWK records and fields Get started with GAWK AWK language fundamentals Page 12 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks Record 1 Field 0 cocoa Record 2 Field 0 Prince Jef pirhi e
10. use the open source GAWK interpreter to write and execute AWK programs so that you can search and manipulate your data in various ways Objectives This tutorial is written for anyone who wants to begin harnessing the text manipulation power of AWK In this tutorial you use GAWK to learn the various methods of running AWK programs You also see how programs are structured and learn AWK s record and field paradigm By the time you have completed the tutorial you will have learned the rudimentary aspects of the language including formatting output record and field manipulation and pattern matching You should also be able to write custom AWK programs to perform complex text processing from the UNIX command line Prerequisites This tutorial has no particular prerequisites although you should be familiar with using a UNIX command line shell Some familiarity with the constructs of the c programming language is helpful but it is not required System requirements You must have a working copy of GAWK installed on your system preferably Version 3 0 or later GAWK is easily obtainable in both source and binary packages see Resources If you re installing GAWK from source consult the README file in the GAWK source distribution which lists any additional software requirements for successful compilation and installation Section 2 Get ready to GAWK Learn about the AWK programming language and the differences between implementations and
11. Get started with GAWK AWK language fundamentals Begin learning AWK with the open source GAWK implementation Skill Level Intermediate Michael Stutz stutz dsl org Author Consultant 19 Sep 2006 Discover the basic concepts of the AWK text processing and pattern scanning language This tutorial gets you started programming in AWK You ll learn how AWK reads and sorts its input data run AWK programs manipulate data and perform complex pattern matching When you re finished you ll also understand GNU AWK GAWK Section 1 Before you start Learn what to expect from this tutorial how to get the most out of it and what you need to work through it About this tutorial GNU AWK GAWK is an open source implementation of the venerable AWK programming language and it is available for all UNIX systems The AWK language is a UNIX standby a powerful text manipulation and pattern matching language that is particularly suited for information retrieval making it ideal for use with today s database driven applications Because of its integration with the UNIX environment complete working programs can be conceived built and executed quickly with immediate results This tutorial provides a hands on introduction to the AWK text processing language Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 1 of 23 developerWorks iobm com developerWorks It shows how to
12. at home with the c like syntax of AWK s input language In fact many of its features including control statements and string functions such as printf and sprintf appear virtually identical However some differences do exist Versions of AWK The AWK language was updated and more or less replaced in the mid 1980s with an enhanced version called NAWK New AWK The old AWK interpreter still exists on many systems but it s often installed as the oawk Old AWK command while the NAWK interpreter is installed as the main awk command as well as being available as nawk Dr Kernighan still maintains NAWK like GAWK it is open source and freely available see Resources GAWK is the GNU Project s open source implementation of the AWK interpreter While the early GAWK releases were replacements for the old AWK it has since been updated to contain the features of NAWK In this tutorial AWK always refers to references general to the language while those features specific to the GAWK or NAWK implementations are referred to by their names You ll find links to GAWK NAWK and other important AWK sites in the Resources section GAWK features and benefits GAWK has the following unique features and benefits e Itis available for all major UNIX platforms as well as other operating systems including Mac OS X and Microsoft Windows e Itis Portable Operating System Interface POSIX compliant and contains all features from the 1992 POSIX sta
13. ches range patterns match text across records It outputs the full records that contain part of the match For instance searching for a range of Heigh to folly outputs the text of the first two records awk Heigh folly sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Output whole paragraphs for matches If you make the field separator the newline character and you make the record separator a null string AWK treats entire paragraphs as single records This effectively makes it a paragraph grep outputting whole paragraphs containing matches to your search This functionality can be useful on files containing large texts Search for green in the sample file after redefining the separators Without redefining them this search outputs only the first record which is the first line But because the entire sample file is a single paragraph the match outputs the whole file itself awk BEGIN FS n RS green sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then Neigh hop the holly Section 7 Wrap up In this tutorial you ve begun to use GAWK the GNU Project s open source Get started with GAWK AWK language fundamentals Page 20 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks implementation of the AWK programming languag
14. e You ve learned the rudiments of the AWK programming language including how to run and structure programs and basic operations such as field and record manipulation and pattern matching There s a lot more to learn AWK is truly one of the great UNIX power tools but even at your first exposure you ve been able to feel the power of the AWK language as a tool for text manipulation Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 21 of 23 developerWorks iobm com developerWorks Resources Learn Effective management of system logs developerWorks March 2006 This article describes a simple application of AWK and Extensible Markup Language XML to show UNIX system data in a reader friendly way GAWK Effective AWK Programming Read the standard user manual for GAWK AIX and UNIX Visit the developerWorks AIX and UNIX zone to expand your UNIX skills New to AIX and UNIX Visit the New to AIX and UNIX page to learn more about AIX and UNIX developerWorks technical events and webcasts Stay current with developerWorks technical events and webcasts AIX 5L Wiki A collaborative environment for technical information related to AIX Podcasts Tune in and catch up with IBM technical experts Get products and technologies GAWK source code Download a free copy of the latest from the GNU Project FTP site IBM AIX Toolbox for Linux Applications A co
15. e manner and you can use it to match fields that do not contain a given pattern field pattern Try printing only records in the sample data whose third field contains an s character S awk 3 s sample Most friendship is feigning most loving mere folly To print the full names of all users whose login shell is not bash use awk BEGIN FS 7 bash print 5 etc passwd Use boolean operators You can combine patterns with the boolean operators as shown in Table 3 and you can combine boolean operators in a single rule Table 3 GAWK boolean operators Operator Description amp amp Logical AND operator Logical OR operator NOT operator Try printing the fourth field of only those records from the sample data that match the regexps in the and to awk in amp amp the amp amp to print 4 sample Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 19 of 23 developerWorks iobm com developerWorks UAto Now print records from the sample data that do not contain holly or that do contain most while changing the output record separator to a hyphen awk BEGIN OFS holly most print 1 2 sample Most friendship Use range patterns Use the comma between two patterns to specify a range meaning all the text between both patterns and the patterns themselves Unlike other sear
16. ern and then performs the given action on those records pattern action You can omit either the pattern or the action in a rule Get started with GAWK AWK language fundamentals Page 6 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks Actions consist of AWK statements and are separated by semicolons You can give multiple rules on the same line too but then you must separate them with semicolons as well When a rule only contains an action it s performed on every record in the input When a rule only contains a pattern the records that match those patterns are printed to the output The empty pattern matches the null character and it is the same as giving a rule with no pattern at all However when the empty action is given it s not the same as giving no action at all An empty action specifies doing nothing and therefore the record is not printed Print each record of the input You can write a rule to print each and every record of input in a few ways most simply as This is effectively the same as peime Formally you could do i A preine This is about the simplest program in AWK While it doesn t do anything spectacular programs not much bigger than this can perform very complex operations Use the BEGIN and END patterns AWK contains two special patterns BEGIN and END Both are given without slashes The BEGIN patt
17. ern specifies actions to be performed before any records are processed BEGIN action The END pattern specifies actions to be performed after all records are processed END action BEGIN is frequently used to set variables END is often used to tabulate total and process data and figures that were read in the various input records Together these patterns are often used to output text before and after the processed input text is output Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 7 of 23 developerWorks iobm com developerWorks For example you can output messages when the program begins and right before it ends as in the AWK program given in Listing 3 Listing 3 A program with BEGIN and END patterns Program to print a file with a header and footer BEGIN print Beginning of file print Hi Giz Beint avery line im tha rile ENDER O See peine Vaad ciles Notice that statements are separated by semicolons and that program comments begin with a hash character Some essential actions You typically build actions with AWK language statements such as the print statement in Listing 3 Table 1 lists some of the most common GAWK statements and functions used in actions and describes their meanings For c programmers note the similarities between the statements and functions of the language and
18. f e gt Field 8 As described in Elements of an input file you can reference an entire record with 0 which includes all fields and field separators This is the default value for many commands So for example print as you ve done before is the same as print 0 both commands print the entire current record Print specific fields To output a certain field give the name of that field as an argument to print Try printing the first field in every record in the sample file Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 13 of 23 developerWorks iobm com developerWorks awk print 1 sample Heigh ho Moist Then You can give multiple fields in a print statement and they can be in any order S awk print 7 3 1 sample holly heigh ho Heigh ho mere is Most the Then Notice that some lines don t have a seventh field in such cases nothing is printed When separated by a comma the fields are output with spaces between them You can concatenate them by omitting the comma To print the seventh and eighth fields concatenated together use S awk print 7 8 sample woki s merefolly You can combine quoted text with fields Try this awk print Field 2 2 sample ieilel 2e Saline Field 2 friendship Field 2 heigh ho You should already be getting an idea of the power of working
19. k POSIX or GNU style options program file POSIX options GNU long options f progfile file progfile F iS field separator fs v var val assign var val i ae vaL W compat compat W copyleft copyleft W copyright GOP ELENE W dump variables file dump variables file W gen po CSO W help help W lint fatal lint fatal SW aine e mnte old W non decimal data non decimal data W profile file profile file W posix 00S W re interval re interval W source program text source program text W traditional traditional W usage Useqe W version version To report bugs see node Bugs in gawk info which is section Reporting Problems and Bugs in the printed version Get started with GAWK AWK language fundamentals Page 4 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks As you can see GAWK takes the GNU standard option for getting the version The output you get including a notice from the Free Software Foundation concerning the licensing of GAWK and its lack of warranty should look like Listing 2 Listing 2 Displaying the GAWK version gawk version GNU Awk 3 1 5 Copyright C 1989 1991 2005 Free Software Foundation This program is free software you can redistribute it and or modify it under the terms of the GNU General Public License as published by the
20. llection of open source and GNU software built for AIX 5L for IBM Systems System p systems and IBM RS 6000 that includes GAWK NAWK Like GAWK the original AT amp T distributed by Brian Kernighan is also open source IBM trial software Build your next development project with software for download directly from developerWorks Discuss Participate in the AIX and UNIX forums e AIX 5L technical e AIX for Developers Forum e Cluster Systems Management IBM Support Assistant e Performance Tools technical e Virtualization technical e More AIX and UNIX forums Get started with GAWK AWK language fundamentals Page 22 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks e Participate in the developerWorks blogs and get involved in the developerWorks community About the author Michael Stutz Michael Stutz is author of The Linux Cookbook which he also designed and typeset using only open source software His research interests include digital publishing and the future of the book He has used various UNIX operating systems for 20 years You can reach him at stutz dsl org Trademarks Linux is a registered trademark of Linus Torvalds in the United States other countries or both Microsoft Windows Windows NT and the Windows logo are trademarks of Microsoft Corporation in the United States other countries or both UNIX is a registered trademark of The O
21. nd of file Besides the practicality of typing programs of any length running AWK programs at the command line has a caveat you must be careful with quoting In AWK Get started with GAWK AWK language fundamentals Page 10 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks variables such as 1 represent fields as described in the next section in many shells these fields are special variables that translate to the arguments given at the command line As a filter AWK is frequently used as a text filter in a pipeline This is where GAWK reads its data from the standard input awk program Try testing it with your sample file cat sample awk print Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly From a file In practice only one liners are ever run from the command line Large GAWK programs are always in a file Use the f option to specify the program file So assume that a file named progfile contains the following arime You get the same output you would when running awk at the command line when you run this awk f progfile sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly Notice that when you have the program in a file there s no need for shell
22. ndard e It has no predefined memory limits e Helpful new built in functions and variables are available Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 3 of 23 developerWorks iobm com developerWorks e It contains special regexp operators e Record separators can contain regexp operators e Special file support is available to access standard UNIX streams e Lint checking is available e It uses extended regular expressions by default e It allows unlimited line lengths and continuations with the backslash character e It has better more informative error messages e It includes TCP IP networking functions Check your version After you have installed GAWK you must first determine where your local copy has been placed Most systems use GAWK as their primary AWK install such as usr bin awk as a symbolic link to usr bin gawk so that awk is the name of the command for the GAWK interpreter This tutorial assumes such an installation On systems with another flavor of AWK already installed or taking precedence you might have to call GAWK as gawk You ll know that you have everything installed correctly if you type awk and get the GNU usage screen as shown in Listing 1 Most other flavors of AWK return nothing at all Listing 1 GAWK installed as awk awk Usage gawk POSIX or GNU style options f progfile file Usage gaw
23. pen Group in the United States and other countries Other company product or service names might be trademarks or service marks of others Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 23 of 23
24. r from its default a newline character to anything you d like Its current value is kept in the Rs variable Change the record separator to a comma and try it on the sample file awk BEGIN RS sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly Change the output AWK output is handled just like AWK input data and it is divided into fields and records the output stream has its own separators which are initially set to the same defaults as the input separators spaces and newlines The output field separator used in print statements in which fields are separated by commas is set to a single space and you can change it by redefining the oF Ss variable The output record separator is set to a newline character and you can change it by redefining the ORS variable To strip all newlines from a file and place all the file s text on a single line which is useful for certain kinds of textual analysis and filtering just change the output record separator to the null character Try it on the sample file S awk BEGIN ORS sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly Every newline is stripped out including the last The returning shell prompt is on the same line as the output data To add a final newline put it in an END rule
25. the AWK equivalents Table 1 Common GAWK statements Statement Description exit Stops the execution of the program and exits next Stops processing the current record and immediately advances to the next record nextfile Stops processing the current file and immediately advances to the next file print Prints quoted text records fields and variables The default is to print the entire current record printf Prints formatted text similar to its C counterpart but the trailing newline must be specified sprintf Returns as a string as formatted text using the same format as printf Section 4 Running GAWK programs GAWK takes two input files the command file containing the AWK program itself and the data file s to work on You need some sample data so use a text editor to place the entire contents three lines of Listing 4 into a file called sample Get started with GAWK AWK language fundamentals Page 8 of 23 Copyright IBM Corporation 1994 2008 All rights reserved ibm com developerWorks developerWorks Listing 4 Sample text Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly Methods of running GAWK programs You can run GAWK programs in any of four ways at the command line as a filter from a file or as a script At the command line You don t have to keep commands in a file You can pass them as arguments This is
26. the common method of running GAWK one liners The format is awk program filespec Try this one liner to print every line of the sample file awk print sample Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly This program reads in the file sample and prints each record in other words it just outputs the entire file verbatim To GAWK the data in the file looked like Figure 3 Figure 3 GAWK s interpretation of the sample file Get started with GAWK AWK language fundamentals Copyright IBM Corporation 1994 2008 All rights reserved Page 9 of 23 developerWorks ibm com developerWorks Record 1 RS Heigh ha sing heigh ha unto the green holly Record 2 Most friendship is feigning most loving mere folly Record 3 Then heigh ho the holly Because GAWK takes multiple input files this program concatenates multiple files if you specify them as arguments One liners aren t limited to programs that fit on a single line You could for instance quote all of Listing 3 on the command line and the program runs the code in Listing 5 Listing 5 A multiple line one liner awk BEGIN print Beginning of file END print Wo Ug print End of file sample Beginning of file Heigh ho sing heigh ho unto the green holly Most friendship is feigning most loving mere folly Then heigh ho the holly E
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